1. Field of the Invention
The present invention relates to a screw with a screw head wherein an engaging concavity is defined, in particularly to accommodate different screw bits.
2. Description of the Related Art
A conventional screw is disclosed by U.S. Pat. No. 2,402,342 in FIGS. 1 and 2, generally includes a head 11, a shank 12 with threads 13. An engaging concavity 111 is defined in a top of the head 11 surrounded by four recesses 112. Each recess 112 includes an end surface 113 and two insides 114 and an opening with a width smaller than said end surface. Due to the limitation of recess number, the screw head only suits for Phillip and slotted screw bit. Further, the recesses 112 are easily broken when the torque focuses on the junction of recesses and central portion.
Refer to U.S. Pat. No. 2,445,978 in FIGS. 3 and 4, a conventional screw generally includes a head 31, a shank 32 with threads 33. An engaging concavity 311 is defined in a top of the head 31 surrounded by six lobes 312. Each lobe 312 includes an end surface 313 and two insides 314 and an opening which has a width equal to the width of the end surface 313. Said two insides 314 are paralleled to each other leading the screw bits easily slip from the engaging concavity 311.
Refer to U.S. Pat. No. 5,364,212 in FIG. 5, a conventional screw generally includes a head 41, a shank 42 with threads 43. An engaging concavity 411 is defined in a top of the head 41 surrounded by four recesses 412. Each recess 412 includes an end surface 413 and two insides 414. Two circumferential faces 415 are further defined between any two adjacent recesses 412. Due to the unique structure of engaging concavity, only particular screw bits can engage the engaging concavity to drive the screw.
The present invention intends to provide a screw head wherein a plurality of radial recesses is defined, each recesses includes two insides without paralleling to each other so as to receive the screw bits with different shapes and sizes